Field
The described technology generally relates to a substrate for transparent flexible display and an organic light-emitting diode display including the same.
Description of the Related Technology
A transparent flexible display uses a polymer substrate that functions as a backplane of an organic light-emitting diode (OLED). The substrate can include a colored polymer substrate and a transparent polymer substrate.
The colored polymer substrate has good thermal resistance (e.g. >450° C.) and mechanical properties by forming a charge transfer complex (CTC). A representative example can be a colored polyimide film.
The transparent polymer substrate is made by restricting formation of the CTC into a film. In order to form a transparent polymer film, a functional group with strong electro negativity is introduced into the polymer such as —CF3 and —SO2, which causes the π electron density in a chain to be reduced. And a bulky group is introduced in a polymer chain and steric hindrance can occur.
However, in the case of a flexible display device including a colored polymer substrate, since the colored polymer forms the CTC and absorbs visible light wavelengths in a visible ray area, a yellow film is formed after coating and hardening. It then becomes difficult to apply the colored polymer substrate itself in a transparent flexible device because of a large yellow index.
On the other hand, in the case of a transparent polymer applied flexible display device, it is desirable to have the existing processing temperature (<400° C.) be reduced because of the reduction in thermostable property according to the restriction on the formation of the CTC.
Consequently, research is being conducted to identify the technology that can implement a transparent flexible display by tuning the colored polymer substrate.